Retreiving element face number in binary .ply file
Ok so here is the script that worked for me:

import bmesh
me = bpy.context.object.data
bm = bmesh.from_edit_mesh(me)

for v in bm.verts:
    if v.select:
        lf = v.link_faces
        face_indices = [f.index for f in lf]
        print(face_indices)